Low Spec Computer Normal Baking Tips?
Blender is genereally faster if you do not view the UVs of a high poly object while at the same time working with the mesh in 3d. UV mapping a high poly object might not be necessary, it is better to avoid doing that at all and work with UVs only on the lower poly versions that you bake the normals for. You can also hide parts of the mesh while working - in edit mode h to hide selected, Shift+h to hide unselected, alt+h to unhide. You can hide objects you do not need to see in the object mode as well it might be easier to do this from the Outliner or use local mode(Numpad /) to concentrate on one object. Spliting your object into smaller objects where possible and working on parts at a time might also make a difference. Obviously viewing objects in textured or material modes is slower than in solid or wireframe modes. 

It's worth considering that the best cure for slow hardware might still be upgrading the hardware - no matter how much we don't want to hear that. If it's earning you money it's worth it, if not, than do you really need to work with such high poly meshes or is it possible to settle for less?..